NORFOLK, VA. — The sailor who was fatally shot Monday while trying to stop a civilian gunman has been identified as Master-at-Arms 2nd Class Mark Mayo, who put himself in harm’s way to save a shipmate, the Navy confirmed Wednesday.

Officials said Mayo, 24, who was serving as the chief of the guard Monday night, rushed from his post after seeing a civilian storm the destroyer Mahan and struggle with the ship’s petty officer of the watch, in the process stripping the watchstander’s weapon. Mayo ran to the quarterdeck and placed himself between the civilian — who was “behaving erratically,” according to a Navy news release issued Wednesday — and the Mahan‘s petty officer of the watch. Mayo’s actions shielded the POOW from the civilian’s gunshot; the civilian, a trucker with base access, was later killed by the Mahan’s topside rover.

“Petty Officer Mayo’s actions on Monday evening were nothing less than heroic. He selflessly gave his own life to ensure the safety of the Sailors on board USS Mahan,” said Capt. Robert Clark Jr., the commanding officer of Naval Station Norfolk, said in a Wednesday statement. “Petty Officer Mayo’s family has endured a tremendous loss, as have the men and women of Naval Station Norfolk, in the loss of a shipmate and friend.”

Adm. Bill Gortney, the head of Fleet Forces Command, on Wednesday appointed Rear Adm. Jeffrey Harley to lead an investigation into the circumstances surrounding the deadly shooting. Harley is president of the Board of Inspection and Survey.

“Our thoughts and prayers go out to the family, friends and shipmates of our sailor who was killed Monday night,” Gortney said. “I have directed a second investigation to be conducted in addition to the law enforcement investigation led by Naval Criminal Investigative Service.”

The second investigation will be convened under the Manual of the Judge Advocate General. It will be a comprehensive examination into the circumstances surrounding the shooting, to include a review of applicable policy, programs and implementation, the Navy said in a release.

The male civilian gained access to Naval Station Norfolk with proper credentials while driving a tractor-trailer onto the base Monday and then gained access to Pier 1, which has a watchstander who checks IDs.

Mayo, a Hagerstown, Md., native, enlisted in the Navy in October 2007 and reported to Naval Station Norfolk in May 2011, according to Navy personnel records. He had been advanced to MA2 on June 16, 2012. He had previously served in at Rota, Spain, and Bahrain.

His awards include the Good Conduct Award, National Defense Service Medal, Global War on Terrorism Expeditionary Medal, Global War on Terrorism Service Medal and Navy Marine Corps Overseas Ribbon.